1. Field of the Invention
The present invention relates to power-line-operated inverter-type power supplies for gas discharge lamps, especially of a type drawing power from the power line with a high power factor and with only a small amount of third harmonic current components.
2. Description of Prior Art
To provide a substantially constant-magnitude high frequency output current, an inverter-type ballast for a gas discharge lamp normally requires to be supplied with a nearly constant-magnitude DC voltage; and, when powered from a DC voltage obtained by straight-forward rectification and filtering of ordinary 60 Hz power line voltage, such a power supply draws current from the power line with a rather poor power factor.
Power factor correction is sometimes provided; but the associated power factor correction circuitry ordinarily involves the use of rather costly, bulky and energy-robbing 60 or 120 Hz inductors.
In particular, power supplies for gas discharge lamps must provide to such lamps an operating current of fairly low crest factor; yet, to be acceptable in most commercial applications, such power supplies must draw power from the power line with a high power factor as well as with a minimum amount of third harmonic current components.